1. Field of the Invention
The present invention relates to an SLR (single lens reflex) digital still camera, and in particular it relates to an internal reflection prevention mechanism therefor.
2. Description of the Related Art
In an SLR digital still camera proposed by the assignee of the present application, a quick return mirror is made entirely from a half mirror, wherein upon viewing, light transmitted through the half mirror is made incident on a CCD, so that the photometering operation (brightness measuring operation) and the focusing operation (object distance measuring operation) can be carried out based on the output of the CCD; and upon photographing, the half mirror is moved and retracted from the light path, so that all of the light bundles can be directly made incident on the CCD, without loss of light by the half mirror.
In the proposed SLR digital still camera in which the quick return mirror is a half mirror, there is a problem with internal reflection by the half mirror upon photographing. Namely, if the quick return mirror is not a half mirror, it is possible to coat the rear surface thereof with an anti-reflection layer; however, difficulties occur when subjecting the half mirror to an anti-reflection coating treatment. Consequently, in a photographing position in which the half mirror is retracted from the photographing light path, the light reflected by the rear surface of the half mirror reaches the CCD, thus causing flare to occur.
In a known SLR camera which uses a silver-halide type film, the quick return mirror is only provided with a half mirror on the center portion thereof, for the photometering or focusing operation. Furthermore, an auxiliary mirror is provided to reflect the light passing through the half mirror. Upon photographing, the half mirror portion is covered by the auxiliary mirror to thereby prevent the internal reflection.
However, in the above-mentioned SLR digital still camera proposed by the assignee of the present application, no auxiliary mirror is provided and hence the conventional internal reflection prevention mechanism mentioned as above cannot be adopted.
The primary object of the present invention is to provide an apparatus for preventing internal reflection by the quick return mirror upon photographing in an SLR digital still camera which includes: a photographing lens, a quick return mirror made from a half mirror, and a CCD located at the focal plane; wherein upon viewing, the quick return mirror is located in a photographing light path to make the light carrying an object image transmitted through the photographing lens incident on a finder optical system, and upon photographing, the quick return mirror is retracted from the photographing light path to make the object light incident on a focal plane.
According to an aspect of the present invention, there is provided an SLR digital still camera including: a photographing lens; a quick return mirror made of a half mirror which is movable between a viewing position and a photographing position, the quick return mirror being located (in the viewing position) in a photographing light path to make light carrying an object image transmitted through the photographing lens incident on a finder optical system, and in the photographing position, being retracted from the photographing light path to make the object light incident on a CCD located in a focal plane of the camera; an anti-reflection plate which is movable close to, or away from, a rear surface of the quick return mirror; and an anti-reflection plate driving mechanism which moves the anti-reflection plate to a retracted position in which the anti-reflection plate is retracted from the photographing light path when the quick return mirror is in the viewing position, and to a cover position in which the anti-reflection plate extends along the rear surface of the quick return mirror when the quick return mirror is in the photographing position.
Since the anti-reflection plate is positioned underneath the quick return mirror when at the retracted position, internal reflection of light rays from the quick return mirror cannot occur, thereby preventing flare from occurring in the CCD.
Preferably, the anti-reflection plate driving mechanism includes: a first stationary shaft to which one end of the quick return mirror is mounted; a connecting rod which is mounted at one end thereof to a second stationary shaft, the connecting rod extending substantially in parallel with the quick return mirror; first and second movable shafts which are provided at the other end of the quick return mirror and the other end of the connecting rod, respectively; and a connecting link which connects the first and second movable shafts. The anti-reflection plate is made integral with the connecting link; the first and second stationary shafts and the first and second movable shafts are located at positions which define four corners of a parallelogram; and the anti-reflection plate extends in a direction substantially parallel with the optical axis and is located in the retracted position in which the anti-reflection plate is out of the photographing light path when the quick return mirror is in the viewing position, and is located to extend along the rear surface of the quick return mirror when the quick return mirror is in the photographing position.
According to another aspect of the present invention, the anti-reflection plate driving mechanism includes: a first stationary shaft to which one end of the quick return mirror is mounted; a connecting rod which is mounted at one end thereof to a second stationary shaft and which extends substantially in parallel with the quick return mirror; first and second movable shafts which are provided at the other end of the quick return mirror and the other end of the connecting rod, respectively; and a connecting link which connects the first and second movable shafts. The anti-reflection plate includes a main anti-reflection plate which is made integral with the connecting link and an auxiliary anti-reflection plate which is pivoted at the free end of the main anti-reflection plate with respect to the first movable shaft. The first and second stationary shafts and the first and second movable shafts are located at positions which define four corners of a parallelogram. The main anti-reflection plate extends in a direction substantially parallel with the optical axis and is located in the retracted position in which the main anti-reflection plate is out of the photographing light path when the quick return mirror is in the viewing position, and the main anti-reflection plate is located to extend along the rear surface of the quick return mirror when the quick return mirror is in the photographing position. The auxiliary anti-reflection plate is located in a retracted position in which the auxiliary anti-reflection plate is out of the photographing light path and extends in a direction substantially perpendicular to the main anti-reflection plate when the quick return mirror is in the viewing position, and the auxiliary anti-reflection plate is located to extend in the same direction as the main anti-reflection plate in a substantially same plane along the rear surface of the quick return mirror when the quick return mirror is in the photographing position.
This alternative arrangement allows the CCD to be positioned closer to the anti-reflection plate, and thereby facilitating miniaturization.
Preferably, the auxiliary anti-reflection plate is continuously biased to be substantially flush with the main anti-reflection plate, the connecting link being provided with a pressing member which forces the auxiliary anti-reflection plate, against the biasing force, into the retracted position whereby the auxiliary anti-reflection plate is approximately perpendicular to the main anti-reflection plate when the quick return mirror is in the viewing position.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 10-266845 (filed on Sep. 21, 1998) which is expressly incorporated herein by reference in its entirety.